In Terms of the Relationship Between a Therapist's Professional Background

In terms of the relationship between a therapist's professional background and therapeutic efficacy, researchers have found that

A) most individuals show the best progress when they are treated by a clinical psychologist.
B) most individuals show the best progress when they are treated by a certified psychiatrist.
C) most individuals show the best progress when they are treated by a therapist trained in multiple approaches.
D) there is no reliable connection between a therapist's professional background and therapeutic efficacy.